Simulators are known for simulating the behavior of aircraft, land vehicles such as racing or rally cars, and other machinery. Such simulators are used for training or entertainment, and typically comprise a motion platform system which supports equipment such as a pilot's or driver's seat and associated controls. One or more video screens represent the view through the windscreen of the vehicle. The motion platform system operates to move the motion platform to simulate the effects of acceleration on the driver or pilot. These simulated effects are coordinated with the view on the video screen or screens, and may simulate the effects on the pilot or driver of accelerations resulting from gravity, centrifugal forces, acceleration and braking, etc. resulting from inputs to the controls as well as ‘external’ factors such as road surface or contour, or turbulence.
An example of a motion platform system is disclosed in US 2002/0055086, and comprises a motion platform supported by connecting arms through which motion is transmitted to the platform from electric drive motors. The drive motors receive signals from software controlling the simulator to move the platform into a sequence of positions corresponding to the simulated effects to be achieved. US 2002/0055086 discloses a six-axis motion platform system, and so is capable of moving the platform in translation and rotation with respect to an orthogonal coordinate frame of reference. The system thus has six degree of freedom, namely three translational and three rotational degrees of freedom.
The drive motors act on the connecting arms through crank arms which are capable of 360° rotation about the axis of output shafts of the drive motors. During operation of the simulator, very high loads are applied on the crank arms by the connecting arms, and these apply substantial bending moments to the output shafts. Furthermore, the connecting arms not only pivot relatively to the crank arms about pivot axes parallel to the output shaft axis, but also swing inwards and outwards as the motion platform undergoes translational displacement under the action of the other connecting arms.
In order to accommodate the complex interrelated motions of the connecting arms of the system, it has been necessary for the connecting arms to be relatively long, which results in a relatively large height of the motion platform above the base of the system. There is a demand for this height to be reduced, but this requires a reduction in the length of the connecting arms, which in turn causes the connecting arms to undergo a greater range of pivotal movement relative to the respective crank arms. This can cause the movement envelopes of the connecting arms to clash with other parts of the system. The risk of clashing can be reduced by extending the length of crank pins by which the connecting arms are connected to the crank arms, but this increases the moment arm of the bending moments applied by the connecting arms to the output shafts of the drive motors. This increases the loading applied to bearings supporting the output shafts and so can lead to early bearing failure. An alternative solution to the problem is to program the software to restrict the range of movement of the motion platform to positions which do not cause interference between the control arms and other parts of the system. This reduces the versatility of the system, and also requires physical hard stops to be provided to limit movement should excursions from the permitted movement envelope occur as a result of component failure or programming error.